Apparatus for determining gravity



Nov. 14, 1939. A, R. LINDBLAD APPARATUS FOR DETERMINING GRAVITY FiledNov. 24

Patented Nov. 14, 1939 UNITED STATES 2,179,892 APPARATUS ron. nltrnamnvcGltAvirlr Axel auaolf undbloa, slookholm, sweden, gu-

lignor to Boliden: Gruvaktiebolag, Stockholm,

Sweden, a 'Joint-stock 'Sweden company of Applloatlon November 24, 1937,sonal No. 170,353

In Sweden September 30, 1937 The present invention relates to animproved temperature regulation mechanism i'or determining gravity orchanges in the same with the ald of a movable body whose weight has beenbal- 54 anced by means oi' a spring mechanism, and the invention ischaracterized essentially thereby that the movable body with itssuspension mechanism is altogether encased ina vessel with a' large heatcapacity and of a material with good l heat conductivity, this vessel inits y turn being altogether encased in a Dewar vessel (thermos "ask).

It is generally known to apply heat 'regulating covers or casings aroundgravimeters, but none of the designs hitherto used is now satisfactory.For of late years the precision of measuring has been raised to apreviously unimagined degree. Instruments with 0.05 mgal (milliga1)precision of measurement can at present be con- 2'0 structed but, inorder to enable the sensitiveness of these apparatus to be utilized itis necessary that the sensitiveness of these apparatus can be kept withthe utmost precision at the desired level and practically constant.Variations of as little as o ne hundredth degree or so disturb or spoilthe measurement result.

In order to attain the precision now so necessary the mechanismaccording to the present invention is combined so as to encasealtogether the movable parts of the gravimeter in a closed metal vesselwith large heat capacity with the arrangement to encase the whole ofthis apparatus, i. e., the measurement vessel containing the movableparts of the gravimeter in a Dewar vessel (thermos ask). Furthermore, itis advisable and suitable, to provide the metal vessel with an electricwinding and an automatic temperature regulator.

In order to explain and elucidate the essential 4o and material pointsof the present invention there is shown on the accompanying drawing anexample according to which the apparatus can be suitably arranged.

'I'he movable body I is suspended in a stand 2 by means of the twosprings 3, so that the body in case of a change of the gravity can movein a vertical direction. The body is at its upper part shaped like'aplate 4, which together with an insulated plate l fastened in the stand,forms a condenser whose capacity is changed with the changes in theposition of the body. The elements I to 5 are made from metal. Ihe plate5 is fastened to the metal body by means of insulating interlining. Bymeasuring the variations of the capacity of the condenser 4, 5 in movingthe apparatus from one place to another there is obtaineda relativeexpression of the change in the magnitude of the gravity at thediii'erent places of observation. The measuring of the capacity of thecondenser can be done 5 with the aid of a 'capacity gauge suitable forthe purpose connected up between the lines 6 and 1, line i beingconnected up with the stand 2, which via the springs 3 is conductivelyconnected with the-body I and the plate I, and the line 1, which l0 -isconnected to the insulated plate i.

In order to avoid variations in temperature the movable body I with thestand 2 is altogether encased in a -closed metal vessel 8 with greatheat; capacity, provided with a heating device 1l made as an electricwindingv 8 round the upper part of the vessel and through the lines 'I0and II connected'to the battery 23. The electric current in the winding9 is regulated by the thermoregulator I2, which in the drawing is 20represented as a bimetal regulator. 'I'his regulator is connected by theline I3 with the grid in the electron tube I6. The anode circuit of thelatter, which is fed with current from the battery I1, is connected upto the electromagnet 25 I8. Through the contact I9, which is keptpressed by the spring 20 against the plate 2 I, the current is appliedto the heating winding 9 and the vessel 8 is heated. The contact I9 isprovided with a projection 22 consisting of iron or 30 nickel. Duringheating the bimetallic leaves of the thermoregulator approach oneanother until contact occurs. The grid of the electron tube thenreceives a positive voltage which ampliiles the current in the anodecircuit and thereby 35 strengthens the iield surrounding theelectromagnet to such an extent that the contact I9 is attracted and thecurrent in the heating winding 8 is interrupted.

When cooling has proceeded so far that the 40 thermoregulator circuit isinterrupted, the current in the anode circuit again becomes so weak thatthe spring is able to overcome the magnetic eld and to press the contactI9 against the plate 2| so that the current can again flow to the 45heating winding. l

The whole measurement ve'ssel l is in its turn placed in a Dewar vesselI4, which is closed with a plug I5, made of a heat-insulating material,e. g., cork or fiber mass, with passages for 50 any necessary wires.

Havingv thus described my invention, I declare that what I claim is:

1. An apparatus for measuring directly the variations in the force orgravity comprising in 55 rent supplied to the electric heating coil tomaintain a substantially constant temperature within the closure.

2. An apparatus for measuring directly the variations in the force ofgravity comprising in combination a condenser, means operable' bygravimetric force for varying the capacity of said condenser, a closure`of heat conducting material for said condenser, an electrical heatingcoil without but in contact with said closure, and an automaticthermoregulator intimately connected with said closure and adapted tocontrol the current supplied to the electric heating coil to maintain asubstantially constant temperature within the closure, said automaticthermoregulator comprises bimetal regulator means operating against oneanother.

3. An apparatus for measuring directly the variations in the force ofgravity comprising in combination a condenser, means operable bygravimetric force for Varying the capacity of said condenser, a closureof heat conducting material for said condenser, an electrical heatingcoil without but in contact with said closure, means for controlling theheating current supplied to said coil to maintain a substantiallyconstant temperature within the closure and a Dewarvessel (thermosflask). enclosing the entire apparatus to effect a single unit of whichthe temperature of the operating elements can be controlled to theaccuracy required when measuring small variations in gravimetric force.

4. An apparatus for measuring directly the variations in the force ofgravity comprising in combination a condenser, means operable bygravimetric force for varying the capacity of said condenser, a closureof heat conducting material for said condenser, an electrical heatingcoil without but in Contact with said closure, an electric relay toeiect the control of the heating current supplied to the electricalheating coil, said relay being regulated by a thermoregulator intimatelyconnected with the inner closure, said thermoregulator operating on therelay by means of an electron tube, whereby the temperature Within theclosure can be maintained substantially constant.

AXEL RUDOLF LINDBLAD.

